topic Re: Get smallest extent from a list of rasters - different approach in Python Questions

Get smallest extent from a list of rasters - different approach

Andreas — Fri, 22 Jan 2016 11:44:11 GMT

Original thread located here: Get smallest extent from a list of rasters

I had issues with that method, if some extents do not overlap, arcgis extent is "empty" while the above minof is (always?) still a rectangle!
In the docs it is said thats minof is the intersection of inputs. But that seems not to be a Intersect_analyst-equivalent. I tried with three extent objects, two do not overlap and one overlaps all other.

Message was edited by: Xander Bakker (branched to new thread)

Re: Get smallest extent from a list of rasters - different approach

XanderBakker — Fri, 22 Jan 2016 12:17:42 GMT

Could you elaborate on what the desired output should be based on the three rasters you mentioned?

Re: Get smallest extent from a list of rasters - different approach

DanPatterson_Retired — Fri, 22 Jan 2016 13:45:45 GMT

From environment settings Output Extent (Environment setting)—Help | ArcGIS for Desktop

With intersection of inputs...

Intersection of Inputs—The extent where all input features or rasters overlap (intersect one another). Note that it is possible that none of the features overlap and that a null extent (zero width and height) may result. In such cases, no features will be processed.

Re: Get smallest extent from a list of rasters - different approach

XanderBakker — Fri, 22 Jan 2016 15:01:42 GMT

True, and that's what the script from the original post did. That's why I would like to hear what the desired output should be, to see if something can be created to match that...

Re: Get smallest extent from a list of rasters - different approach

Andreas — Sun, 24 Jan 2016 14:43:55 GMT

Thank you for your contribution,

I got an extent "between" the non-overlapping rasters, but it should be none, i think.

The Problem araised with a tool that shoud calculate a hexagonal fishnet, where the extent is provided by the user, with an extent parameter in a script tool. Now my question was how to calculate the extent, if the parameter value is MINOF and was glad to see your solution. If i use a tool, like Copy_management and an MINOF in environments extent, the tool creates no output, because the two of three extents do not overlab. But this isn't possible to get with the approach above?

I attached a new sketch to show what i got.

Andreas

Re: Get smallest extent from a list of rasters - different approach

DanPatterson_Retired — Mon, 25 Jan 2016 00:26:51 GMT

not sure

yellow blue intersect produces max-X and max-Y for MIN-OF

purplish blue intersect produces min-X and min-Y for MIN-OF

IF min-of is your left-over bit

Now I am wondering if the order affects the results. overlay blue last...

order as yellow, purple then blue

compare to

blue, then yellow, purple

Re: Get smallest extent from a list of rasters - different approach

Andreas — Mon, 25 Jan 2016 11:29:03 GMT

Luc Pinner said that max(minx), max(miny), min(maxy), min(maxy) would be the MINOF-extent,

but if you read arcgis-docs it says it would be the "intersection of inputs" where all inputs overlap.

So, if they don't overlap, the extent should be None. But with the calculation above i always get an extent, it can't be "none". I'm looking for a prcedure that gives me the same result as If i use the minof extent in the tool environment (processing extent). But i don't know how to do it.

In the environment settings you can't set an order and if you calculate a min or a max order doesn't matter either. Do you mean arcgis may use an ordered set of extents? Too bad we can't see an output of the processing extent...

Re: Get smallest extent from a list of rasters - different approach

DanPatterson_Retired — Mon, 25 Jan 2016 11:37:06 GMT

What I was suggesting is that you try it yourself during the selection process... it may be easier to control the order through scripting... buy you can compare using the procedure I described instead of using all three at once, do the process incrementally and in different orders.

Re: Get smallest extent from a list of rasters - different approach

XanderBakker — Sat, 11 Dec 2021 06:35:33 GMT

If the calculation was done by collecting all the minx, miny, maxx and maxy and use the resulting mins and maxs as points to construct the extent, the result will be as you showed in your image. This is however, as you concluded yourself, not the correct result.

Let's take a look at the code below that shows what happens:

import arcpy

def main():
    ext1 = arcpy.Extent(1, 0, 9, 5)
    ext2 = arcpy.Extent(0, 1, 10, 10)
    ext3 = arcpy.Extent(0, 6, 6, 12)

    print "getIntersectingExtent", getIntersectingExtent([ext1, ext2, ext3])
    print "getMinsMaxsExtentsAsExtent", getMinsMaxsExtentsAsExtent([ext1, ext2, ext3])

def getIntersectingExtent(lst):
    ext = lst[0]
    for e in lst[1:]:
        if ext.overlaps(e) or ext.contains(e) or ext.within(e) or ext.equals(e):
            ext = getOverlapExents(ext, e)
        else:
            return None
            break
    return ext

def getOverlapExents(ext1, ext2):
    return getMinsMaxsExtentsAsExtent([ext1, ext2])

def getMinsMaxsExtentsAsExtent(lst):
    xmin = max([e.XMin for e in lst])
    xmax = min([e.XMax for e in lst])
    ymin = max([e.YMin for e in lst])
    ymax = min([e.YMax for e in lst])
    return arcpy.Extent(xmin, ymin, xmax, ymax)

if __name__ == '__main__':
    main()

The result of the code is:

getIntersectingExtent None
getMinsMaxsExtentsAsExtent 1 5 6 6 NaN NaN NaN NaN

Both use the same procedure where the min and max of the extents is determined. However, the first result will test is there is overlap and then determine the minimums and maximums. The second will simply determine the minimums and maximums of the extents and when provided to the arcpy.Extent() method this will correct for minimums being larger than maximums.

Re: Get smallest extent from a list of rasters - different approach

XanderBakker — Sat, 11 Dec 2021 06:35:37 GMT

Just noticed that you cannot simply use the arcpy.Extent().overlaps to check for intersection. You need to evaluate contains, within and equals too.

Something like this:

def extentIntersects(ext1, ext2):
    if ext1.overlaps(ext2) or ext1.contains(ext2) or ext1.within(ext2) or ext1.equals(ext2):
        return true
    else:
        return False

Re: Get smallest extent from a list of rasters - different approach

XanderBakker — Sat, 11 Dec 2021 06:35:40 GMT

... or one can use the polygon property of the extent and use the intersect method of the polygon like this:

import arcpy
ext1 = arcpy.Extent(1, 1, 4, 4)
ext2 = arcpy.Extent(2, 2, 5, 5)
print ext1.polygon.intersect(ext2.polygon, 4).extent

which returns:

2,00000190734863 2,00000190734863 4,00000190734863 4,00000190734863 NaN NaN NaN NaN

It will return:

1,#QNAN 1,#QNAN 1,#QNAN 1,#QNAN NaN NaN NaN NaN

... when there is no intersecting polygon.

Re: Get smallest extent from a list of rasters - different approach

DanPatterson_Retired — Mon, 08 Feb 2016 01:31:18 GMT

Xander... and to add... make sure there is a defined coordinate system or the extent values will be returned in single precision rather than double as evidenced by your examples.

Re: Get smallest extent from a list of rasters - different approach

Andreas — Mon, 08 Feb 2016 08:51:21 GMT

This looks really good, thought about something like this, but had no success. Do you think it is "enough", testing the overlaps in a single for-loop? If I understand the code right, you take the first extent and compare to it to the remaining. For example if the first extent in list overlaps all others, but the second does not overlaps the third. Could we somehow "sort" the polygons or should we use a nested for-loop to check every combination. I tend to look inside an open source product to find a similar operation...

Re: Get smallest extent from a list of rasters - different approach

Andreas — Mon, 08 Feb 2016 10:49:29 GMT

I tried out a few example extents: It works, order seems not to be important.

So, thank you very, very much for contributing your code!

Re: Get smallest extent from a list of rasters - different approach

XanderBakker — Mon, 08 Feb 2016 11:17:06 GMT

To explain a bit what the loop pretends to do:

It takes the first element of the list of extents and uses it as the initial extent
Then it starts to loop through the other extents (element 2 until n)
if there is overlap between the initial extent and the other extent, it determines the intersecting extent
then it continues with the next extent and checks overlap with the intersecting extent
and so on.

There is no need to validate overlaps (intersects) between all extents. If in some situation there is no intersect, it will abort the loop and return None (which you should check for).

Re: Get smallest extent from a list of rasters - different approach

Andreas — Mon, 08 Feb 2016 11:22:16 GMT

So true, that's why you store the return of getOverlapExtents in ext, oversawed this... clever!

Re: Get smallest extent from a list of rasters - different approach

XanderBakker — Mon, 08 Feb 2016 11:22:20 GMT

Could you mark the post that answered your question as the correct answer? This way other members will be able to find the answer to similar question more easy. Thank you!

Re: Get smallest extent from a list of rasters - different approach

DanPatterson_Retired — Mon, 08 Feb 2016 13:03:18 GMT

you should then mark Xander's correct ... assumed answered ... is usually used by moderators, not by people who post questions

Re: Get smallest extent from a list of rasters - different approach

Andreas — Mon, 08 Feb 2016 13:10:49 GMT

I tried before, the only option I had was "richtige Antwort" (correct answer) and then it gets "assumed answered"...

Re: Get smallest extent from a list of rasters - different approach

DanPatterson_Retired — Mon, 08 Feb 2016 13:34:55 GMT

you fixed it...