I've got a fairly simple PathGeometry:
M567764.539,5956314.087L567815.077,5956179.775L567821.625,5956182.314L567773.425,5956311.248L567858.513,5956349.923L567950.858,5956392.466L567949.039,5956399.843L567942.252,5956396.685L567873.018,5956364.467L567799.816,5956330.421L567771.226,5956317.186L567764.539,5956314.087
Now when I query the PathGeometry.Bounds attribute for this data I get the following bounds:
567764.5625,5956180 567950.875,5956400
The expected bounds would be:
567764.539,5956179.775 567950.858,5956399.843
My main problem: the bounds are smaller than the geometry, so parts of the geometry might be outside the bounds.
I create the PathGeometry and show the bounds like this:
PathGeometry geo = PathGeometry.CreateFromGeometry(Geometry.Parse("M567764.539,5956314.087L567815.077,5956179.775L567821.625,5956182.314L567773.425,5956311.248L567858.513,5956349.923L567950.858,5956392.466L567949.039,5956399.843L567942.252,5956396.685L567873.018,5956364.467L567799.816,5956330.421L567771.226,5956317.186L567764.539,5956314.087"));
System.Diagnostics.Trace.WriteLine(geo.Bounds);
What am I doing wrong?
And, more important, how do I get the right bounds for a PathGeometry?
At some point, I would think WPF has to convert to single point for rendering, and I wonder if the value of Bounds is based off of the rendered result. In this case, you're probably seeing a precision limitation based off of the large numbers you're using. I noticed that your Y values were a factor of 10 larger than X, and coincidentally the error was also a factor of 10 larger than the error in X.
If it's possible to subtract off the min X and Y before creating the PathGeometry, I think you'll get better numbers. Assuming you're displaying the PathGeometry, you could place it in a Canvas and apply Canvas.Left/Top to your values to get the right offset on screen. To get the correct bounds, you would then add the Top/Left offsets to the result of your Bounds.
Just a reminder that there's a bit of speculation in this answer. I haven't looked at the innerworkings of Bounds, but the relative error seems to point to a conversion to and from floats.
I think you're seeing the imprecision due fact that the numbers PathGeometry is made up of large floating point numbers.
I'm not sure if you'll be able to obtain the precision that you need.
You will probably have to compare the bounds using an acceptable tolerance, like:
bool isMatch = (Math.Abs(MyPath.Bounds.X - ExpectedBounds.X) < TOLERANCE);
where you can set the TOLERANCE to 0.25 or something.
Related
Selecting a random color on a computer is a touch harder than I thought it would be.
The naive way of uniform random sampling of 0..255 for R,G,B will tend to draw lots of similar greens. It would make sense to sample from a perceptually uniform space like CIELUV.
A simple way to do this is to sample L,u,v on a regular mesh and ensure the color solid is contained in the bounds (I've seen different bounds for this). If the sample falls outside embedded RGB solid (tested by mapping it XYZ then RGB), reject it and sample again. You can settle for a kludgy-but-guaranteed-to-terminate "bailout" selection (like the naive procedure) if you reject more then some arbitrary threshold number of times.
Testing if the sample lies within RGB needs to be sure to test for the special case of black (some implementations end up being silent on the divide by zero), I believe. If L=0 and either u!=0 or v!=0, then the sample needs to be rejected or else you would end up oversampling the L=0 plane in Luv space.
Does this procedure have an obvious flaw? It seems to work but I did notice that I was rolling black more often than I thought made sense until I thought about what was happening in that case. Can anyone point me to the right bounds on the CIELUV grid to ensure that I am enclosing the RGB solid?
A useful reference for those who don't know it:
https://www.easyrgb.com/en/math.php
The key problem with this is that you need bounds to reject samples that fall outside of RGB. I was able to find it worked out here (nice demo on page, API provides convenient functions):
https://www.hsluv.org/
A few things I noticed with uniform sampling of CIELUV in RGB:
most colors are green and purple (this is true independent of RGB bounds)
you have a hard time sampling what we think of as yellow (very small volume of high lightness, high chroma space)
I implemented various strategies that focus on sampling hues (which is really what we want when we think of "sampling colors") by weighting according to the maximum chromas at that lightness. This makes colors like chromatic light yellows easier to catch and avoids oversampling greens and purples. You can see these methods in actions here (select "randomize colors"):
https://www.mysticsymbolic.art/
Source for color randomizers here:
https://github.com/mittimithai/mystic-symbolic/blob/chromacorners/lib/random-colors.ts
Okay, while you don't show the code you are using to generate the random numbers and then apply them to the CIELUV color space, I'm going to guess that you are creating a random number 0.0-100.0 from a random number generator, and then just assigning it to L*.
That will most likely give you a lot of black or very dark results.
Let Me Explain
L* of L * u * v* is not linear as to light. Y of CIEXYZ is linear as to light. L* is perceptual lightness, so an exponential curve is applied to Y to make it linear to perception but then non-linear as to light.
TRY THIS
To get L* with a random value 0—100:
Generate a random number between 0.0 and 1.0
Then apply an exponent of 0.42
Then multiply by 100 to get L*
Lstar = Math.pow(Math.random(), 0.42) * 100;
This takes your random number that represents light, and applies a powercurve that emulates human lightness perception.
UV Color
As for the u and v values, you can probably just leave them as linear random numbers. Constrain u to about -84 and +176, and v to about -132.5 and +107.5
Urnd = (Math.random() - 0.5521) * 240;
Vrnd = (Math.random() - 0.3231) * 260;
Polar Color
It might be interesting converting uv to LChLUV or LshLUV
For hue, it's probably as simple as H = Math.random() * 360
For chroma contrained 0—178: C = Math.random() * 178
The next question is, should you find chroma? Or saturation? CIELUV can provide either Hue or Sat — but for directly generating random colors, it seems that chroma is a bit better.
And of course these simple examples are not preventing over-runs, so they color values to be tested to see if they are legal sRGB or not. There's a few things that can be done to constrain the generated values to legal colors, but the object here was to get you to a better distribution without excess black/dark results.
Please let me know of any questions.
I have a Columndiagram. This diagram may have Y values from 0 to very larg numbers.
My problem:
When the Y values are small (from my observation smaller than 7), the chart shows double values. (for example: 0, 0.01, 0.02 ... , 0.1), which is in my case not correct.
What I want:
force the Y Axis to use integers.
What I cannot do:
I cannot define a seperator for the Y axis and set its Step to 1. Becuase if I do it, I'll have Step= 1 even if the values are very large, which is not desirable.
Is there any workaround for it?
By default, the library decides the step (when you don't force it) with the CalculateSeparator() method (for more info see this), since the library should also allow you to plot decimal values, it can not be forced to display only integers.
A simple work around I can think of, is to force the Axis.MaxValue property.
In your case, when your values are less than 7, I would force the Axis.MaxValue to 10 (or any other value that works fine for you), then when the data in your chart is greater than 7, you can set Axis.MaxValue back to double.NaN and the library will calculate this limit by it self.
I hope it helps you.
I have a "FlattenedPathGeometry" and I want to be able to get a specific point.X from the path based on a specific Point.Y
Basically I just need the X value at any given Y.
Thanks in advance for any help.
GetFlattenedPathGeometry gives you back a polygonal so basically you have to consider loop all the points and calculating the minimum distance to your point.
If you can make any assumption on the Geometry shape or your point, you can speed up the search.
For example if the path is very long, you can speed up by intersecting the shape with a circle/square centered in your point. This limit the number of points of the shape to test but be careful that the intersection method is very expensive. You'll have to measure the performances with a stopwatch to understand what's better in your case.
I have custom control - chart with size, for example, 300x300 pixels and more than one million points (maybe less) in it. And its clear that now he works very slowly. I am searching for algoritm which will show only few points with minimal visual difference.
I have a link to the component which have functionallity exactly what i need
(2 million points demo):
I will be grateful for any matherials, links or thoughts how to realize such functionallity.
If I understand your question correctly, then you are looking to plot a graph of a dataset where you have ~1M points, but the chart's horizontal resolution is much smaller? If so, you can down-sample your dataset to get about the number of available x values. If your data is sorted in equal intervals, you can extract every N'th point and plot it. Choose N such that the number of points is, say, double the resolution (in this case, N=2000 will give you 500 points to display).
If the intervals are very different from eachother (not regularly spaced), you can approximate your graph with a polynomial, or spline or any other method that fits, and then interpolate 300-600 points from that approximation.
EDIT:
Depending on the nature of the data, you may end up with aliasing artifacts when you simply sample every N't point. There are probably better methods for coping with this problem, but again - it depends on what exactly you want to plot.
You could always buy the control - it is for sale!
John-Daniel Trask (Co-founder of Mindscape ;-)
When rendering huge visuals in WPF, the visual gets distorted and more distorted with increasing coordinates. I assume that it has something to do with the floating point data types used in the render pipeline, but I'm not completely sure. Either way, I'm searching for a practical solution to solve the problem.
To demonstrate what I'm talking about, I created a sample application which just contains a custom control embedded in a ScrollViewer that draws a sine curve.
You can see here that the drawing is alright for double values <= 2^24 (in this case the horizontal coordinate value), but from that point on it gets distorted.
The distortion gets worse at 2^25 and so the distortion continues to increase with every additional bit until it just draws some vertical lines.
For performance reasons I'm just drawing the visible part of the graph, but for layouting reasons I cannot "virtualize" the control which would make this problem obsolete. The only solution I could come up with is to draw the visible part of the graph to a bitmap, and then render the bitmap at the appropriate point - but there I have again the precision problem with big values, as I cannot accurately place the bitmap at the position where I need it.
Does anybody have an idea how to solve this?
It is not WPF's fault.
Floating point numbers get less and less precise the farther from zero they are - it is a cost of stuffing enormous data range (-Inf, +Inf) into 32 (float) / 64 (double) bits of data space. Floats actually become less precise than integer at around 2^30.
64bit integers have constant spacing (1), but have limited range of −9,223,372,036,854,775,808 to +9,223,372,036,854,775,807.
You may also consider using Decimal type (which however has also limited value range).
(update: oh didnt see how old this post was... i guess i clicked the wrong filter button in stack overflow...)
The relative precision is relevant here. So just saying "look 2^24 is fine and 2^25 is not" is not enough information. You said it is a sin, thus I guess y-axis max and min never changes between those pictures. So y-axis doesnt matter. Furthermore the x-step size stays the same, i guess? But you did not tell us the sin period length or the x-step size, you chose. That is relevant here. The relative precision of the x-size steps becomes worse when you go to higher x-values, because the x-step-size becomes too small relativly to the x-value itself.
precision of c# floating point types:
https://learn.microsoft.com/de-de/dotnet/csharp/language-reference/builtin-types/floating-point-numeric-types
example:
x-step size = 1.
x = 1 (no problem)
x = 1000 (no problem)
x = >2^23 (32 bit starts to get problems with step size = 1; 64 bit no problems yet)
x = >2^52 (64 bit starts to get problems with step size = 1)