# Optimal Texture Resolution?

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Hi.I have a question about optimal texture resolution for resample.exe.I know that 4.8m/pixel is almost optimal one, but I think this is fornorth-south direction only. For east-west direction, 4.8m/pixelis not optimal, because LOD13 tile is not square.I think optimal resolution is 6.4 * cos(latitude) m/pixel for east-west direction. Is this correct?

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This question inevitably draws us closer to a more basic question - is FS World flat?LOD grid, at any level, can accomodate a 256x256 data set. At Level 13, under CUSTOM directive, it accomodates a 256x256 pixel bitmap. What FS does to this bitmap (as far as resolution) at higher latitudes, is open for debate...

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I think FS World is 'globally' sphere rather than flat(but may be flat 'locally'...), bacause:1) In FS 2002 SDK (Create Trraining.doc, Advanced topic), LOD grid boundaries are measured in angle, not length.2) I tested scenery creation at very high latitude, and all pixels in resulting texture are very magnified for X-axis (west-east direction).

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Regardless of whether or not the FS is flat or a sphere, each LOD13 area takes a 256 pixel X 256 pixel texture. In order to get the greatest resolution possible for my textures I don't worry at all about the meters per pixel resolution, but concern myself with the pixels per degree.When I work on a scenery area I start with as high a resolution photograph as my computer will take. From a practical standpoint 4 meters per pixel is adequate. I then identify on the photo 4 corners that are on the LOD13 grid. They will not necessarily line up on the corners of a true rectangle. Then I stretch the image so that the LOD13 corners match the corners of a rectangle. (I use Adobe Photshop for this. I don't know if PaintshopPro can do this.) It can be any rectangle as long as the LOD13 corners are now at the corners of a true rectangle. (This is basically projecting the image onto a cylindrical projection, instead of the UTM projection of most photos.) Then resize the image to match 256 pixels for each LOD13 area. I typically work on a LOD9 area that is 16 x 16 LOD 13 areas so the final image is 4096 x 4096 pixels, but I have a fast machine with lots of RAM (1GB). When you work this way adjacent areas match up extremely well.Misho, I don't know how well you do photo manipulation with your programming skills, but being able to have TB take four points of an area and orthorectify and resize the area of the photo to match the resolution for textures would be the easiest way to get the photos correctly located. Users then would only need to be able to identify on the photo four corners, and the program would do all their computations for them. They wouldn't have to rotate or resize an image, and any resolution image could be used.I am not much of a programmer, but I am an engineer and could help with the math and developing an algoritm.Frank

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Hi Frank."I don't worry at all about the meters per pixel resolution, but concern myself with the pixels per degree"Absolutely right! :)If our photos were in Geographic projection ( pixels/degree ), there would be no problems. But the original post is correct. Resample deals in degrees, and the width of pixels/meter narrow near the poles, and fatten at the equator, while the pixels/degree remain a constant width.As far as optimal resolution? I would think you'd want resolution equal to, or finer than, 4m/pixel... resample will "resample" the excess... and does a good job of that.Dick

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Hello to all,Sorry for the wacky idea, but what if it were better to use a lower resolution image?Using 4 meter per pixel (or better) images seems to be the best solution, but the resulting ground texture is still very blurry, even if one sharpens the original image before resampling, as suggested by Paul Leatzaw.In the Niagara Falls example, Microsoft provides images that are 8 meters per pixel. Obviously, this does not give ground textures with a lot of detail, but they are noticeably less blurry than higher resolution images.The default ground textures do not have much detail either, but they are also not as blurry when close as custom textures.So, it would seem heretical to prone the use of lower resolution images, but this trade-off may give the advantage of reducing the dread "blurries" that, in the end, are more annoying than reduced detail.Just wondering if anyone has any ideas on this.Best regards.Luis

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I agree with the observation but do not have an answer..Dick KLBE

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I did say in my first response "From a practical standpoint 4 meters per pixel is adequate.", so I agree there. What I was trying to get to was I would love to see a program with a "4 point calibration" that would then rotate, rectify, and resize the image before it goes through resample. We could then work on original images in whatever projection they are in, and the program would then convert them to a cylindrical or Geographic projection prior to processing by resample. I think someone who understands how to work with image files would be able to do that relatively easily. They should be able to do a high quality conversion of the photo, not just a nearest pixel value conversion. I would try it myself, but my programming skills are rudimentary at best, and I have almost no knowledge of image file structures.As far as images near the equator or the poles, FS stretches or compresses the image horizontally to match the width of the LOD13 area. The assumption posed by Takuya Murakami is correct, that the horizontal resolution at the equator is about 6.35 m/pixel. The vertical resolution stays constant at about 4.76 m/pixel. At about 41.4

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Even if this subject seems to be

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Sounds reasonable. Does this mean that Resample "stretches" the picture to fit the LOD, then distorting the pixel arrangement and creating a blurred image? With PhotoShop can you "manually resize" the picture to equal the calculated m/pixel based on yout LAT/LON?I stopped using an photoreal scenery because the clarity, to me, was always less than the FS2004 synthetic textures. Even expensive Megascenery products that claim a high resolution base source appeared to be not worth the price at low altitudes when compared to generic textures.Dick Boley @KLBE

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Hola Carlos,You are absolutely correct in your calculations. This is something that we have known for quite a while and had been presented in this forum some time ago.Vertical resolution is always about 4.77 meters per pixel, while horizontal resolution will vary depending on your latitude.This means that if you are resizing your image, you should consider doing each dimension independently of the other!Dick raises a good point about the clarity of the images, and this goes back to my remarks above. The default ground textures appear clearer, but not because they have greater resolution. Rather, they have less resolution! All default textures seem to be around 8 meters per pixel. Because of this, they display less "blockiness" when flying close than images with greater resolution and more detail.Best regards.Luis

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Hi Dick,The way I "manually resize" my image is, first, to rectify the image from UTM to Lat/Lon; in this process, the image is distorted (stretched) lightly. Then I compute (with the resolution I proposed) the size (in pixels) of the image to be sent to TB; with Photoshop you can resize your image independently in X and in Y. This final image is, visually, distorted, but when you go to FS the things seem to be in the right place. One trick I use when resizing in Photoshop is to resize with the option "Nearest neighbourhood" activated instead of "interpolation"; in this way the final image on FS is less blurred.I am developing the photorealistic scenery of my province (Alava, in the Basque Country, Spain), and even if the result is not perfect (quite blurry at low altitudes) is best than the default scenery if you are making VFR (I attach the result just if you want to compare with the default scenery)

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Hola LuisThank you for your commment. Maybe Misho could use this information for the new release of the TB.Gracias

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