World building using ArcGIS

[loogie]

lol i found grass earlier this month downloaded it and... well.. didn't touch a thing after that.. i have no idea how to use it, but if i got the basics down, and this type of analysis was available, i'd be happy to

[su_liam]

I was hoping someone who had a basic grounding in using at least one GIS program might be able to help me figure out how to use this thing. It seems promising as hell and you can't beat the price, but I can't even figure out how to load a raster.

The quick starts I've found seem to assume a basic grounding in GIS.

[loogie]

well, if you point out the quick starts i'll take a look and see what i can figure out... i couldn't even turn it on when i looked at it (not that i tried very hard)

it does look promising (acctually better in some respects then a lot of other program i've seen) and of course.. free would make it an amazing addition to a roleplaying cartographers arsenal.

[su_liam]

Here is one good site. I still can't get my own images imported, but at least I've been able to play with Spearfish...

[loogie]

sorry man, i can't even get grass to run

no progress with arcgis as well.. i've been to busy with school..

working on a project that was due this morning at 8am...

oops... once everything slows down i should be ok tho...

[priggs]

GRASS. I get excited every time I read about it, download it, and try to use it... too painful!

[su_liam]

I got frustrated and went back to playing with landserf. Not as capable, but at least I can import my #$@ing pngs and use them as HFs. My original intention was to use landserf to see if I could convert a png HF into something GRASS could see, but I couldn't face the ordeal and played some with landserf's feature extraction and such.

I'm really interested in these flowmaps, so I'm working on a q and d java implementation of a "flowmap." I'm not sure if it's technically a flowmap, it basically just sets the value of each pixel equal to the number of pixels that are directly above it(ie those from which water could flow into it.) I have three models: Greatest Drop('Water' only flows down to the lowest neighbor below a high point. Possibly analogous to SFD?), All Drops('Water' flows to all neighbors below a high point. One possible analog to MFD, perhaps?), Scaled Drop('Water' flows into all neighbors below a high point in a quantity proportional to the change in altitude. That is steeper paths will get more 'flow'. Another possible analog to MFD?) Applying a threshold to the resulting, "flow map," could be used to give a fairly decent idea about rivers. I assume this isn't really a flowmap in the sense GRASS uses the term, because the GRASS flowmap is deadly slow and this should be pretty quick. Initially I thought I'd have to implement a heap to get best performance, but it looks like it would be O(n log n) time whether I use a heap-based priority queue or just sort cell coordinates by height initially. I'm leaning toward the sort-and-go method, because my head just refuses to wrap itself around the bottom up method for building the heap.

It's a sign of how much fun I've had trying to get GRASS to work that I'd rather program my own solution :-)

[loogie]

well arcgis is much simpler to use.. and i'm assuming most of whats in grass is the same if not copied off ESRI (they're the largest, and most used GIS software providers in the world... and i'm working for them! WOOT!)

though i don't know much about the math involved, i know the flow accumulation processes in arcgis have 2 main steps... you must create a flow direction grid(raster) which does what it sounds like you suggest takes every cell in the grid, and finds out which direction water would flow off it (N S E W + diagonals). that takes a short bit of time (i upped my anti in my map and made a new one thats 4096x4096) and in my example it takes about 2-3 mins... the result... isn't all that good for determining rivers (i guess it depends how you display it) but then you run the flow accumulation, which (from what i can disern) will go through the raster cell by cell and total those directions... so as one raster flows into another the next value is 2, the next is 3 etc etc... that takes a long time... i started running it about 10 mins ago now and its still going... last time i did it on a raster less then half the size i left and had some food, before coming back

those tasks don't seem terribly difficult to preform (generally most GIS is simple, its just that by hand it would take forever, by a computer, its fast) but the other thing that makes arcgis' tools so great is their options, for instance, flow accumulation can be weighted, meaning you can add acctual precipitation data to the formula, and get fairly accturate water fall results... as well as do other things (thats the only thing i could really think of)

the GIS tools will definitely help with many aspects, from finding trails, viewsheds (thanks for the ideas, never thought of em!) as well as doing climate modeling, and finding the best locations for various plants and animals.

now, if i only had the time to acctually do it

[priggs]

You're not alone in preferring to program rather than try to learn GRASS. I do all my spatial modeling using a combination of Python/Numpy/GDAL/OGR/Shapely/SQLite. I liked Arc/Info and ArcView 3.2, but not ArcGIS. Even though I have a copy on a Windows computer in the lab, all I use it for is to look at maps and export them to Adobe Illustrator as soon as possible. I'll quit using it totally (except probably for teaching, can't find a way out of that yet) as soon as either Quantum GIS is further improved or I finish programming my Mac GIS visualizer.