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Author Topic: Tutorial: Make your own forest shading/landcover  (Read 8395 times)

Boyd

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Re: Tutorial: Make your own forest shading/landcover
« Reply #15 on: May 23, 2013, 11:03:55 AM »
Pretty cool - thanks.  :) But I'm on GM 12 and have decided to sit out a few upgrades since it really does everything I need at this point.

BTW, if anyone is playing around with this, I made a couple small tweaks that I think produce better results. First, when I select all the features in the "Residential" layer, I am use primary BLUE as a color instead of RED like the tutorial. This seems to create a more accurate boundary between the forest and populated areas. Since red and green are complimentary colors, I *think* this was creating a gray zone between areas after blending in Photoshop and gray is closer to the black pallete color, therfore creating a gap.

The other difference is that I am up-sampling the raster export at 30 feet per pixel instead of 50 feet per pixel in the tutotial. This makes for less noticeable stair-steps as you zoom in on the finished map. At 50 feet/pixel the landcover starts to look pretty "jaggy" zooming in closer than .3 miles in Mapsource. At 30 feet/pixel the jaggies become noticeable when you hit the 500 foot zoom in Mapsource.

Further experimentation would be a good idea if you plan to use this technique, to see what you personally find acceptable. It also depends on other map features. In an area with lots of roads and/or contour lines the jaggies aren't so noticeable.

Also, in areas that are predominately forest you can end up with some huge and very complex green polygons. These are fine until you try to slice and dice them (such as as gridded export). If the polygons are too big and complex, GM messes them up when cropping sometimes. The only fix I have found for this is to work with smaller images to prevent the polygons from getting too large.
« Last Edit: May 23, 2013, 11:06:34 AM by Boyd »

Seldom

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Re: Tutorial: Make your own forest shading/landcover
« Reply #16 on: May 23, 2013, 12:19:13 PM »
Pretty cool - thanks.  :) But I'm on GM 12 and have decided to sit out a few upgrades since it really does everything I need at this point....

Also, in areas that are predominately forest you can end up with some huge and very complex green polygons. These are fine until you try to slice and dice them (such as as gridded export). If the polygons are too big and complex, GM messes them up when cropping sometimes. The only fix I have found for this is to work with smaller images to prevent the polygons from getting too large.

You can still script GENERATE_EQUAL_VAL_AREAS with GM12, just not EQUAL_COLORS.

I'm pretty sure the problem you describe with large wooded areas  processed in PhotoShop is malformed polygons. (Photoshop creates a bowtie where it should have a rectangle.)  If you only process the areas in GM and leave the 30 meter jaggies the polygons will remain well formed.  I slice my wooded areas in GPSmapEdit all the time with no trouble.  When I tried to slice them after PhotoShop the shapes got pretty bizarre.

Boyd

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Re: Tutorial: Make your own forest shading/landcover
« Reply #17 on: May 23, 2013, 01:20:03 PM »
Basically I think you're saying that it's easier to turn a simple image into a polygon than a complex image. Definitely true. But I like the curves that photoshop creates with the up-sampled raster image. I had the same problems big time when I turned shaded LIDAR terrain into polygons.

My standard map tile is a USGS 24k quad. I find that if I cut the NLCD tiff's into about 9 quads (3x3) it works pretty well. I like to think in terms of USGS quads, they have names and there's just something intangible that I like about them. It is also a convenient size to hand-edit. But it can get tedious because they are pretty small. Wouldn't be practical to use my workflow if I were mapping a large state.  ;)

Seldom

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Re: Tutorial: Make your own forest shading/landcover
« Reply #18 on: May 23, 2013, 02:48:56 PM »
I like to think in terms of USGS quads, they have names and there's just something intangible that I like about them.

When I came across the Carcass Canyon and Scorpion Gulch quads, I knew Utah was the right place for me.