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  • How do I best run a search on Date when it is not a :has_many association?

    - by Angela
    I have a number of activities that have a calculated scheduled date. The activities, for example, Email, have a email.days method which is the days from a Contact.start_date on which it should be sent. This means contact.start_date + email.days yields a date on which email is sent to contact. I would like to use link_to around the date, so I can see all the emails and associated contacts that are to be scheduled on that date. However, this "date" is not an attribute or an associate, so I'm not linking to a model's view. It's calculated. So: 1) What should the actual "format" of the date that gets passed in the URl be? What is the method to do the consistent conversion? 2) How do I (find) all instances, because this "date" is not an actual attribute, is it a calculated value which changes depending on the two associated models of Contact and Email. Thanks.

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  • What is viewstate in JSF, and how is it used?

    - by MatthieuF
    In JSF, there is a viewstate associated with each page, which is passed back and forth with submits etc. I know that viewstate is calculated using the states of the various controls on the page, and that you can store it either client side or server side. The question is: how is this value used? Is it used to validate the values sent at submit, to ensure that the same request is not sent twice? Also, how is it calculated - I realise that richfaces may be calculated differently from myfaces, but an idea would be nice. Thanks.

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  • How to Sum calulated fields

    - by Nazero Jerry
    I‘d like to ask I question that here that I think would be easy to some people. Ok I have query that return records of two related tables. (One to many) In this query I have about 3 to 4 calculated fields that are based on the fields from the 2 tables. Now I want to have a group by clause for names and sum clause to sum the calculated fields but it ends up in error message saying: “You tried to execute a query that is not part of aggregate function” So I decided to just run the query without the totals *(ie no group by , sum etc,,,) : And then I created another query that totals my previous query. ( i.e. using group by clause for names and sum for calculated fields… no calculation here) This is fine ( I use to do this) but I don’t like having two queries just to get summary total. Is their any other way of doing this in the design view and create only one query?. I would very much appreciate. Thankyou: JM

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  • How to check value of stored procedure output parameter

    - by Anna T
    I have a stored procedure that: A. inserts some rows into a "table variable" based on some joins B. selects all values from column x from that table into a string with comma separated values C. selects all from the "table variable" If I execute the procedure like this: EXEC CatalogGetFilmDetails2 2,111111; a table is returned as instructed per step C above. How can I execute it so that also the output parameter value is displayed? (see point B above). I need to check if it's calculated properly. And since the second parameter is of output type, meaning it's calculated inside the procedure, why is it mandatory to specify a value for it when executing the procedure? I normally use a random value for it, it anyway doesn't matter/impact the result. On the other hand if I try to execute it without the output parameter, it returns an error) Thank you very much! This is how the procedure starts: CREATE PROCEDURE CatalogGetFilmDetails2 (@FilmID int, @CommaSepString VARCHAR(50) OUTPUT) AS And this is how @CommaSepString is calculated: SELECT @CommaSepString = STUFF((SELECT ', ' + Categ FROM @Filme1 FOR XML PATH('')), 1,1,'')

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  • How do I compare the md5sum of a file with the md5 file (that was available to download with the file)?

    - by user91583
    Images are available for a distro on http://livedistro.org/gnulinux/israel-remix-team-mint-12. I want to use the 32-bit version. I have downloaded the ISO file for the 32-bit version (customdist.iso). I have downloaded the md5 file for the ISO file (customdist.iso.md5). I want to calculate the md5sum of the ISO file and compare it to the md5 file. I can use the md5sum command to display within the terminal the calculated md5 for the ISO file. I have searched the web and can't find a way to compare the calculated md5 for the ISO file with the downloaded md5 file. So far, the closest I have come is the command md5sum -c customdist.iso.md5 from within the folder containing both the files, but this command gives the result: md5sum: customdist.iso.md5: no properly formatted MD5 checksum lines found Any ideas?

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  • Atmospheric scattering sky from space artifacts

    - by ollipekka
    I am in the process of implementing atmospheric scattering of a planets from space. I have been using Sean O'Neil's shaders from http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter16.html as a starting point. I have pretty much the same problem related to fCameraAngle except with SkyFromSpace shader as opposed to GroundFromSpace shader as here: http://www.gamedev.net/topic/621187-sean-oneils-atmospheric-scattering/ I get strange artifacts with sky from space shader when not using fCameraAngle = 1 in the inner loop. What is the cause of these artifacts? The artifacts disappear when fCameraAngle is limtied to 1. I also seem to lack the hue that is present in O'Neil's sandbox (http://sponeil.net/downloads.htm) Camera position X=0, Y=0, Z=500. GroundFromSpace on the left, SkyFromSpace on the right. Camera position X=500, Y=500, Z=500. GroundFromSpace on the left, SkyFromSpace on the right. I've found that the camera angle seems to handled very differently depending the source: In the original shaders the camera angle in SkyFromSpaceShader is calculated as: float fCameraAngle = dot(v3Ray, v3SamplePoint) / fHeight; Whereas in ground from space shader the camera angle is calculated as: float fCameraAngle = dot(-v3Ray, v3Pos) / length(v3Pos); However, various sources online tinker with negating the ray. Why is this? Here is a C# Windows.Forms project that demonstrates the problem and that I've used to generate the images: https://github.com/ollipekka/AtmosphericScatteringTest/ Update: I have found out from the ScatterCPU project found on O'Neil's site that the camera ray is negated when the camera is above the point being shaded so that the scattering is calculated from point to the camera. Changing the ray direction indeed does remove artifacts, but introduces other problems as illustrated here: Furthermore, in the ScatterCPU project, O'Neil guards against situations where optical depth for light is less than zero: float fLightDepth = Scale(fLightAngle, fScaleDepth); if (fLightDepth < float.Epsilon) { continue; } As pointed out in the comments, along with these new artifacts this still leaves the question, what is wrong with the images where camera is positioned at 500, 500, 500? It feels like the halo is focused on completely wrong part of the planet. One would expect that the light would be closer to the spot where the sun should hits the planet, rather than where it changes from day to night. The github project has been updated to reflect changes in this update.

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  • What's the better user experience: Waiting once at startup for a long time or waiting frequently for a short time?

    - by Roflcoptr
    I'm currently design an application that involves a lot of calculation. Now I have generally two possibilities which I have both tested: 1) During startup of the application I calculated only the most important values and these values that consume a lot of time. So the user has to wait approximately 15 seconds during startup. But on the other hand a lot of user interactions require recalculation so that the user often has to wait 2-3 seconds after clicking somewhere until the application has calculated and loaded all values 2) I load everything during startup. This takes from 90 to 120 seconds... This is quite a long time, but the big advantage is that all the user interactions are executed immediately. So what would you generally consider the better approach? Loading all time-consuming operations during startup or when needed?

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  • New videos available #dax #ssas #powerpivot

    - by Marco Russo (SQLBI)
    The collaboration I and Alberto started with Project Botticelli is starting producing content. At this point we have three videos available: DAX in Action shows the power of DAX in PowerPivot solving common patterns not so easy or fast to solve in other languages DAX: Calculated Columns vs. Measures shows the difference between calculated columns and measures in DAX Introduction to DAX has a content corresponding to the title! The first two videos are freely available, the third one is longer and visible only to subscribers. The goal for this series of video is to reach advanced Excel users and BI developers that are new to DAX. If we should categorize this content, it’s a sort of level 200 session in a conference. I don’t expect readers of this blog to watch this video (if not for the sake of curiosity!) but if you have to explain this subject to anyone else and you have other priorities… well, you can add this post to the list of resources you provide for studying the subject!

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  • How do I find the closest points(thereby forming a polygon) enclosing a particular point?(see image)

    - by nilspin
    I am working with a game engine, and my task is to add code for simulating fracture of rigid meshes. Right now I'm only working on breaking a cube. I am using Voronoi's algorithm to make a (realistic)fractured shard and I am using the half-plane method to generate a voronoi cell. Now the way I do this is for every seed point, I make planes that are perpendicular bisector planes(the straight black lines in the image) with rest of the seed points and I calculate the intersections of all these planes to give me distinct points(all the orange dots). I've gotten this far. Out of all these calculated intersection points, I only need the ones that are closest and enclosing the seed point(the points encircled in red) and I need to discard all the rest. Information that I have : 1) Plane equations of all planes(defined by normalized normal vectors and their distance from origin) 2) Points of intersection(that I've calculated) Can anybody help me find out how I can find the points encircled in red? Thanks.

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  • Force netsh/arp binding multicast IP addres with specific MAC address

    - by Olivier
    I would like to setup an binding from an IP address to a MAC address using netsh. Goal is to bond an IP address which is a multicast address (224.224.x.y) to a given MAC address (which is NOT the calculated one from the multicast IP address : 01:00:5e:X:Y:Z It used to work with Windows XP (was it a bug that used to be "perfect" for my needs?), but Windows 7/8/8.1 forces the MAC address to the calculated one instead of letting me put what I want! (http://nettools.aqwnet.com/ipmaccalc/ipmaccalc.php shows MAC address calculation for multicast IP address) Thus I'm doing the following. Listing existing mappings: netsh.exe interface ip show neighbors "Ethernet" Interface 12 : Ethernet Internet address Physical address Type 224.0.0.22 01-00-5e-XX-YY-ZZ static Then adding my interface mapping manually: netsh.exe interface ip add neighbors "Ethernet" "224.xxx.yyy.zzz" "00-80-EE-UU-VV-WW" Finally, listing again my mappings: netsh.exe interface ip show neighbors "Ethernet" Interface 12 : Ethernet Internet address Physical address Type 224.0.0.22 01-00-5e-XX-YY-ZZ static **224.xxx.yyy.zzz 01-00-5e-UU-VV-WW static** As you can see, the MAC Address of the second entry (the one I just made) has been dynamically replaced by the calculated MAC Address corresponding to my IP Address... Calculation is done as follow (and displayed in hexa): UU=(xxx-128) VV=yyy WW=zzz But I don't want that behavior. My IP address and MAC address cannot be changed, and I must associate them accurately. Does anybody know how to disable MAC address substitution/calculation in netsh? Thanks, Olivier.

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  • onFocusChange code example?

    - by Rich
    I have a form with 2 fields where you can enter in either months or years. How do I setup the form so that if you enter in the years, the months edittext field will be automatically calculated and entered into it's own box. Likewise, I want the years to be calculated if you entered in the months Can anyone give me sample code for this?

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  • How to interpret weka classification?

    - by gargi2010
    How can we interpret the classification result in weka using naive bayes? How is mean, std deviation, weight sum and precision calculated? How is kappa statistic, mean absolute error, root mean squared error etc calculated? What is the interpretation of the confusion matrix?

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  • Matlab Correlation Function

    - by Joka
    function letter=read_char(imgn, num_letters) global templates comp=[ ]; for n=1:num_letters sem=corr2(imgn, templates{1,n}); comp=[comp sem]; end vd=find(comp==max(comp)); Can someon please explain what the 'FOR' loop does and how 'vd' is calculated? Also, what is the variable 'comp' and what will it looks like as the array also contains itself and another variable 'sem' which is calculated from the corr2 function. thanks

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  • SQL Server 2005: Insert a row in a table and update the same row

    - by vikas
    eg:table pkey --guid annualpay datefrom dateto--if null means current record percentannualincrease percent annual increase will be calculated only if there is a difference in newly inserted and previously existing last differing value. percentannualincrease = ([newannualpay-just previous pay(if different from current)]/newannualpay)*100 eg newid(),5000,today,null,0--very first row newid(),5000,today+1,null(*),0 newid,5500,today+2,null(*),?????????????--> need to be calculated before insert *--insert will close the previous record by updating dateto=null to todays date How can I do this stuff in a trigger???

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  • SSRS - Sort table based on column value

    - by Ehsan
    I am trying to sort the following table: hYear hSale ------------------------------------ [year] =Count(Fields!sale.Value) The table only has one row group (year) and no column group. I'd like to: -initially sort the table based on the calculated value; is it possible? -add interactive sort to calculated column based on the value. I assume I should sort 'Detail rows', but what will be the sort expression?

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  • How to Count tickets as DateWise

    - by user560716
    I have a query regarding my report, the report format is as under **Date** **Received** **Closed** **Pending** 12/01/10 1000 900 100 12/02/10 2000 1000 1000 12/03/10 1500 1300 200 The above report shows the Help Desk tickets Received, Closed, Pending Count as date wise. How can I create a dynamic SQL query to show above result? Received Tickets is calculated on SubmitedDate Closed Tickets is calculated on ClosedDate with status "Closed" same for Pending Tickets whose status is "Pending". Please provide me the idea or some sample SQL queries.

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  • AI to move custom-shaped spaceships (shape affecting movement behaviour)

    - by kaoD
    I'm designing a networked turn based 3D-6DOF space fleet combat strategy game which relies heavily on ship customization. Let me explain the game a bit, since you need to know a bit about it to set the question. What I aim for is the ability to create your own fleet of ships with custom shapes and attached modules (propellers, tractor beams...) which would give advantages and disadvantages to each ship, so you have lots of different fleet distributions. E.g., long ship with two propellers at the side would let the ship spin around that plane easily, bigger ships would move slowly unless you place lots of propellers at the back (therefore spending more "construction" points and energy when moving, and it will only move fast towards that direction.) I plan to balance all the game around this feature. The game would revolve around two phases: orders and combat phase. During the orders phase, you command the different ships. When all players finish the order phase, the combat phase begins and the ship orders get resolved in real-time for some time, then the action pauses and there's a new orders phase. The problem comes when I think about player input. To move a ship, you need to turn on or off different propellers if you want to steer, travel forward, brake, rotate in place... These propellers don't have to work at their whole power, so you can achieve more movement combinations with less propellers. I think this approach is a bit boring. The player doesn't want to fiddle with motors or anything, you just want to MOVE and KILL. The way I intend the player to give orders to these ships is by a destination and a rotation, and then the AI would calculate the correct propeller power to achive that movement and rotation. Propulsion doesn't have to be the same throught the entire turn calculation (after the orders have been given) so it would be cool if the ships reacted as they move, adjusting the power of the propellers for their needs dynamically, but it may be too hard to implement and it's not really needed for the game to work. In both cases, how would that AI decide which propellers to activate for the best (or at least not worst) trajectory to be achieved? I though about some approaches: Learning AI: The ship types would learn about their movement by trial and error, adjusting their behaviour with more uses, and finally becoming "smart". I don't want to get involved THAT far in AI coding, and I think it can be frustrating for the player (even if you can let it learn without playing.) Pre-calculated timestep movement: Upon ship creation, ALL possible movements are calculated for each propeller configuration and power for a given delta-time. Memory intensive, ugly, bad. Pre-calculated trajectories: The same as above but not for each delta-time but the whole trajectory, which would then be fitted as much as possible. Requires a fixed propeller configuration for the whole combat phase and is still memory intensive, ugly and bad. Continuous brute forcing: The AI continously checks ALL possible propeller configurations throughout the entire combat phase, precalculates a few time steps and decides which is the best one based on that. Con: what's good now might not be that good later, and it's too CPU intensive, ugly, and bad too. Single brute forcing: Same as above, but only brute forcing at the beginning of the simulation, so it needs constant propeller configuration throughout the entire combat phase. Coninuous angle check: This is not a full movement method, but maybe a way to discard "stupid" propeller configurations. Given the current propeller's normal vector and the final one, you can approximate the power needed for the propeller based on the angle. You must do this continuously throughout the whole combat phase. I figured this one out recently so I didn't put in too much thought. A priori, it has the "what's good now might not be that good later" drawback too, and it doesn't care about the other propellers which may act together to make a better propelling configuration. I'm really stuck here. Any ideas?

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  • Collision detection of huge number of circles

    - by Tomek Tarczynski
    What is the best way to check collision of huge number of circles? It's very easy to detect collision between two circles, but if we check every combination then it is O(n^2) which definitely not an optimal solution. We can assume that circle object has following properties: -Coordinates -Radius -Velocity -Direction Velocity is constant, but direction can change. I've come up with two solutions, but maybe there are some better solutions. Solution 1 Divide whole space into overlapping squares and check for collision only with circles that are in the same square. Squares needs to overlap so there won't be a problem when circle moves from one square to another. Solution 2 At the beginning distances between every pair of circles need to be calculated. If the distance is small then these pair is stored in some list, and we need to check for collision in every update. If the distance is big then we store after which update there can be a collision (it can be calculated because we know the distance and velocitites). It needs to be stored in some kind of priority queue. After previously calculated number of updates distance needs to be checked again and then we do the same procedure - put it on the list or again in the priority queue.

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  • Re-using aggregate level formulas in SQL - any good tactics?

    - by Cade Roux
    Imagine this case, but with a lot more component buckets and a lot more intermediates and outputs. Many of the intermediates are calculated at the detail level, but a few things are calculated at the aggregate level: DECLARE @Profitability AS TABLE ( Cust INT NOT NULL ,Category VARCHAR(10) NOT NULL ,Income DECIMAL(10, 2) NOT NULL ,Expense DECIMAL(10, 2) NOT NULL ) ; INSERT INTO @Profitability VALUES ( 1, 'Software', 100, 50 ) ; INSERT INTO @Profitability VALUES ( 2, 'Software', 100, 20 ) ; INSERT INTO @Profitability VALUES ( 3, 'Software', 100, 60 ) ; INSERT INTO @Profitability VALUES ( 4, 'Software', 500, 400 ) ; INSERT INTO @Profitability VALUES ( 5, 'Hardware', 1000, 550 ) ; INSERT INTO @Profitability VALUES ( 6, 'Hardware', 1000, 250 ) ; INSERT INTO @Profitability VALUES ( 7, 'Hardware', 1000, 700 ) ; INSERT INTO @Profitability VALUES ( 8, 'Hardware', 5000, 4500 ) ; SELECT Cust ,Profit = SUM(Income - Expense) ,Margin = SUM(Income - Expense) / SUM(Income) FROM @Profitability GROUP BY Cust SELECT Category ,Profit = SUM(Income - Expense) ,Margin = SUM(Income - Expense) / SUM(Income) FROM @Profitability GROUP BY Category SELECT Profit = SUM(Income - Expense) ,Margin = SUM(Income - Expense) / SUM(Income) FROM @Profitability Notice how the same formulae have to be used at the different aggregation levels. This results in code duplication. I have thought of using UDFs (either scalar or table valued with an OUTER APPLY, since many of the final results may share intermediates which have to be calculated at the aggregate level), but in my experience the scalar and multi-statement table-valued UDFs perform very poorly. Also thought about using more dynamic SQL and applying the formulas by name, basically. Any other tricks, techniques or tactics to keeping these kinds of formulae which need to be applied at different levels in sync and/or organized?

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  • windows 2008r2 SNMP hrStorageSize reporting wrong values

    - by Giannis Nohj
    I'm trying to monitor disks on windows 2008 R2 system, but I'm getting wrong values returned from hrStorageSize and hrStorageUsed for one of the 2 disks the system has. Local disk C: is returning correct values, whereas D: disk, which is an SAN disk, is reporting 32G instead of 500G. Output of snmpwalk -v 2c -c public hostname-01 .1.3.6.1.2.1.25.2 : HOST-RESOURCES-MIB::hrStorageDescr.1 = STRING: C:\ Label: Serial Number 7ff87ca6 HOST-RESOURCES-MIB::hrStorageDescr.2 = STRING: D:\ Label:Data Serial Number dab5b0b9 ... HOST-RESOURCES-MIB::hrStorageAllocationUnits.1 = INTEGER: 4096 Bytes HOST-RESOURCES-MIB::hrStorageAllocationUnits.2 = INTEGER: 4096 Bytes ... HOST-RESOURCES-MIB::hrStorageSize.1 = INTEGER: 35834383 HOST-RESOURCES-MIB::hrStorageSize.2 = INTEGER: 7864320 ... HOST-RESOURCES-MIB::hrStorageUsed.1 = INTEGER: 32460169 HOST-RESOURCES-MIB::hrStorageUsed.2 = INTEGER: 3192302 I have calculated the first disk (C:) size as 136G, which is correct. On the other hand, D: is calculated as 30G, where it should be 500G. I also tried fsutil on the system and the output was correct. Anyone have any ideas?

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  • Database implementation question?

    - by gundam
    consider a disk with a sector size of 512 bytes, 2000 tracks/surface, 50 sectors/track, 5 doubled sided platters, average seek time is 10 msec. Assume a block size of 1024-byte is selected. Assume a file that contains 100,000 records of 100-byte each is to be stored on the disk, and NONE of the reocd can be spanned 2 blocks. How many blocks are needed to store the entire file?? If the file is arranged sequentially on disk, how many surfaces are required?? Now, i have calculated that 10,000 blocks are needed to store 100,000 records. But i am not sure how to find out the answer of the surfaces required. I only calculated the capacity of track is 25KB and capacity of surface is 50,000 KB But I don't know how to calculate the number of surfaces... Could anyone help me how to get the answer? Thanks a lot!!

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  • Database implementation question? [closed]

    - by gundam
    consider a disk with a sector size of 512 bytes, 2000 tracks/surface, 50 sectors/track, 5 doubled sided platters, average seek time is 10 msec. Assume a block size of 1024-byte is selected. Assume a file that contains 100,000 records of 100-byte each is to be stored on the disk, and NONE of the reocd can be spanned 2 blocks. How many blocks are needed to store the entire file?? If the file is arranged sequentially on disk, how many surfaces are required?? Now, i have calculated that 10,000 blocks are needed to store 100,000 records. But i am not sure how to find out the answer of the surfaces required. I only calculated the capacity of track is 25KB and capacity of surface is 50,000 KB But I don't know how to calculate the number of surfaces... Could anyone help me how to get the answer? Thanks a lot!!

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  • Extreme Optimization – Curves (Function Mapping) Part 1

    - by JoshReuben
    Overview ·        a curve is a functional map relationship between two factors (i.e. a function - However, the word function is a reserved word). ·        You can use the EO API to create common types of functions, find zeroes and calculate derivatives - currently supports constants, lines, quadratic curves, polynomials and Chebyshev approximations. ·        A function basis is a set of functions that can be combined to form a particular class of functions.   The Curve class ·        the abstract base class from which all other curve classes are derived – it provides the following methods: ·        ValueAt(Double) - evaluates the curve at a specific point. ·        SlopeAt(Double) - evaluates the derivative ·        Integral(Double, Double) - evaluates the definite integral over a specified interval. ·        TangentAt(Double) - returns a Line curve that is the tangent to the curve at a specific point. ·        FindRoots() - attempts to find all the roots or zeroes of the curve. ·        A particular type of curve is defined by a Parameters property, of type ParameterCollection   The GeneralCurve class ·        defines a curve whose value and, optionally, derivative and integrals, are calculated using arbitrary methods. A general curve has no parameters. ·        Constructor params:  RealFunction delegates – 1 for the function, and optionally another 2 for the derivative and integral ·        If no derivative  or integral function is supplied, they are calculated via the NumericalDifferentiation  and AdaptiveIntegrator classes in the Extreme.Mathematics.Calculus namespace. // the function is 1/(1+x^2) private double f(double x) {     return 1 / (1 + x*x); }   // Its derivative is -2x/(1+x^2)^2 private double df(double x) {     double y = 1 + x*x;     return -2*x* / (y*y); }   // The integral of f is Arctan(x), which is available from the Math class. var c1 = new GeneralCurve (new RealFunction(f), new RealFunction(df), new RealFunction(System.Math.Atan)); // Find the tangent to this curve at x=1 (the Line class is derived from Curve) Line l1 = c1.TangentAt(1);

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  • Optimizing hash lookup & memory performance in Go

    - by Moishe
    As an exercise, I'm implementing HashLife in Go. In brief, HashLife works by memoizing nodes in a quadtree so that once a given node's value in the future has been calculated, it can just be looked up instead of being re-calculated. So eg. if you have a node at the 8x8 level, you remember it by its four children (each at the 2x2 level). So next time you see an 8x8 node, when you calculate the next generation, you first check if you've already seen a node with those same four children. This is extended up through all levels of the quadtree, which gives you some pretty amazing optimizations if eg. you're 10 levels above the leaves. Unsurprisingly, it looks like the perfmance crux of this is the lookup of nodes by child-node values. Currently I have a hashmap of {&upper_left_node,&upper_right_node,&lower_left_node,&lower_right_node} -> node So my lookup function is this: func FindNode(ul, ur, ll, lr *Node) *Node { var node *Node var ok bool nc := NodeChildren{ul, ur, ll, lr} node, ok = NodeMap[nc] if ok { return node } node = &Node{ul, ur, ll, lr, 0, ul.Level + 1, nil} NodeMap[nc] = node return node } What I'm trying to figure out is if the "nc := NodeChildren..." line causes a memory allocation each time the function is called. If it does, can I/should I move the declaration to the global scope and just modify the values each time this function is called? Or is there a more efficient way to do this? Any advice/feedback would be welcome. (even coding style nits; this is literally the first thing I've written in Go so I'd love any feedback)

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  • Eculidean space and vector magnitude

    - by Starkers
    Below we have distances from the origin calculated in two different ways, giving the Euclidean distance, the Manhattan distance and the Chebyshev distance. Euclidean distance is what we use to calculate the magnitude of vectors in 2D/3D games, and that makes sense to me: Let's say we have a vector that gives us the range a spaceship with limited fuel can travel. If we calculated this with Manhattan metric, our ship could travel a distance of X if it were travelling horizontally or vertically, however the second it attempted to travel diagonally it could only tavel X/2! So like I say, Euclidean distance does make sense. However, I still don't quite get how we calculate 'real' distances from the vector's magnitude. Here are two points, purple at (2,2) and green at (3,3). We can take two points away from each other to derive a vector. Let's create a vector to describe the magnitude and direction of purple from green: |d| = purple - green |d| = (purple.x, purple.y) - (green.x, green.y) |d| = (2, 2) - (3, 3) |d| = <-1,-1> Let's derive the magnitude of the vector via Pythagoras to get a Euclidean measurement: euc_magnitude = sqrt((x*x)+(y*y)) euc_magnitude = sqrt((-1*-1)+(-1*-1)) euc_magnitude = sqrt((1)+(1)) euc_magnitude = sqrt(2) euc_magnitude = 1.41 Now, if the answer had been 1, that would make sense to me, because 1 unit (in the direction described by the vector) from the green is bang on the purple. But it's not. It's 1.41. 1.41 units is the direction described, to me at least, makes us overshoot the purple by almost half a unit: So what do we do to the magnitude to allow us to calculate real distances on our point graph? Worth noting I'm a beginner just working my way through theory. Haven't programmed a game in my life!

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