# Potential Projection Mismatch - Help me Code Jedi's! **URL:** \ **Category:** Uncategorized\ **Created:** [May 17, 2022, 7:43pm UTC](https://mapwindow.discourse.group/t/potential-projection-mismatch-help-me-code-jedis/1342 "2022-05-17T19:43:58Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![ericpalmatier](https://avatars.discourse-cdn.com/v4/letter/e/dbc845/32.png) [@ericpalmatier](https://mapwindow.discourse.group/u/ericpalmatier)\ **Post date:** [May 17, 2022, 7:43pm UTC](https://mapwindow.discourse.group/t/potential-projection-mismatch-help-me-code-jedis/1342/1 "2022-05-17T19:43:58Z")
Hello Everybody (dr. Nick accent / Simpsons) I am a year in on my project and I seem to have stumbled on to what could be a very severe issue. I am positive it is something I am simply overlooking, but as a scientist (and not the data kind!) I am a bit out of my depth here. I think my coding prowess can be summed up thusly: " even a broken clock is right twice a day" That being said, Here’s some background. My software is for mapping raw data counts over a geo-rectified image. pretty simple, probably shouldn’t have taken me a year to get to this point, but here I am. The software allows a user to load an image, typically a screen grab from google maps, but it can be anything really. The user can then geo-rectify it using a subroutine. I think My worldfiles are right, but I have two questions. 1. If the user is using google maps imagery, but the AXmap1 projection is set to projection\_WGS84, will that cause an error when displaying the .JPG/.JGW? 2. If you were mathematically computing the Worldfile, using visual basic, How would YOU do it? I’ll show you below what I am doing and explain it best I can. Here is an image that first led me to believe there was an issue with the way my software displays the image. ![google_vs_MWG_SitePad_V2_2](https://global.discourse-cdn.com/free1/uploads/mapwindow1/original/1X/0603f660d30fba49b96e61459a4b8157df63ca20.jpeg) Here you can see I have drawn an outline around the same image of a building, just overlaid in GIMP and the Opacity adjusted so we can see both at the same time. Clearly there is a bit of a rotation. ![google_vs_MWG_SitePad_V2](https://global.discourse-cdn.com/free1/uploads/mapwindow1/original/1X/243e04a0e314c33437f3df2dd46a847dde40730f.jpeg) Here you can see a similar issue. There seems to be a bit of a rotation and a scaling mismatch. ``` For j = 2 To 100 If CalCoord(j, 1) = 0 Then Exit For End If If (CalCoord(j, 3) - CalCoord(j - 1, 3)) = 0 Or (CalCoord(j, 4) - CalCoord(j - 1, 4)) = 0 Then MsgBox("Error: choose wider spaced points", vbOKOnly) Erase CalCoord Exit For End If If j = 2 Then LongXperPixel = Math.Abs((CalCoord(j, 1) - CalCoord(j - 1, 1)) / (CalCoord(j, 3) - CalCoord(j - 1, 3))) LatYperPixel = Math.Abs((CalCoord(j, 2) - CalCoord(j - 1, 2)) / (CalCoord(j, 4) - CalCoord(j - 1, 4))) Else ' not a true average, fix later LongXperPixel = (LongXperPixel + Math.Abs((CalCoord(j, 1) - CalCoord(j - 1, 1)) / (CalCoord(j, 3) - CalCoord(j - 1, 3)))) / 2 LatYperPixel = (LatYperPixel + Math.Abs((CalCoord(j, 2) - CalCoord(j - 1, 2)) / (CalCoord(j, 4) - CalCoord(j - 1, 4)))) / 2 End If Next j LongXMax = CalCoord(1, 1) - (CalCoord(1, 3) * LongXperPixel) LatYMaX = CalCoord(1, 2) + (CalCoord(1, 4) * LatYperPixel) ' save to world file absoluteYPixel = (-(Math.Abs(LatYperPixel))) absoluteXPixel = (Math.Abs(LongXperPixel)) WorldFileWriter(absoluteXPixel, absoluteYPixel, LongXMax, LatYMaX, mMapFile) regpts = 1 If MsgBox("World File (.JGW) Generated, Click 'OK' to reload SitePad with new rectified image", 1, "World File Generated Sucessfully!") = vbCancel Then 'the user hits cancel. do nothing...idiots.. Else HALTandRESTART() End If ``` I am really confused. I am somewhere between thinking there is an issue with my projection setup, OR I am goofing something up with my Worldfile math. What I have not been able to do, YET, is find a reliable and free piece of software where I could georeference this image and compare the generated Worldfile with mine. Any suggestions would be welcome! ---
**Author:** ![jerryfaust](https://yyz2.discourse-cdn.com/free1/user_avatar/mapwindow.discourse.group/jerryfaust/32/378_2.png) [@jerryfaust](https://mapwindow.discourse.group/u/jerryfaust)\ **Post date:** [May 23, 2022, 6:12am UTC](https://mapwindow.discourse.group/t/potential-projection-mismatch-help-me-code-jedis/1342/2 "2022-05-23T06:12:03Z")
Hello @ericpalmatier Although you may find help here related to imagery and world files, I will suggest an alternative. All of the imagery operations in MapWinGIS are performed by an open-source library that we have incorporated, called GDAL (see [https://gdal.org/index.html](https://gdal.org/index.html)). You may be better off asking this question on their support forum ([https://gdal.org/community/index.html#mailing-list](https://gdal.org/community/index.html#mailing-list)). Respectfully. Jerry. ---
**Author:** ![ericpalmatier](https://avatars.discourse-cdn.com/v4/letter/e/dbc845/32.png) [@ericpalmatier](https://mapwindow.discourse.group/u/ericpalmatier)\ **Post date:** [May 24, 2022, 1:51pm UTC](https://mapwindow.discourse.group/t/potential-projection-mismatch-help-me-code-jedis/1342/3 "2022-05-24T13:51:08Z")
Jerry, Thanks for the insight, I will look through their literature to see what I can find. As a side question, can I access the GDAL tools through the mapwingis API, or will I have to load the GDAL API separately? thanks! ---
**Author:** ![jerryfaust](https://yyz2.discourse-cdn.com/free1/user_avatar/mapwindow.discourse.group/jerryfaust/32/378_2.png) [@jerryfaust](https://mapwindow.discourse.group/u/jerryfaust)\ **Post date:** [May 25, 2022, 6:33pm UTC](https://mapwindow.discourse.group/t/potential-projection-mismatch-help-me-code-jedis/1342/4 "2022-05-25T18:33:02Z")
Yes, there are a number of GDAL operations exposed through the API. See [HERE](https://www.mapwindow.org/mapwingis/class_gdal_utils.html) and related operations in the help file. Regards, Jerry. ---
**Author:** ![ericpalmatier](https://avatars.discourse-cdn.com/v4/letter/e/dbc845/32.png) [@ericpalmatier](https://mapwindow.discourse.group/u/ericpalmatier)\ **Post date:** [May 25, 2022, 8:46pm UTC](https://mapwindow.discourse.group/t/potential-projection-mismatch-help-me-code-jedis/1342/5 "2022-05-25T20:46:44Z")
Jerry, You are an amazing person! Thanks for pointing me in this direction, this is precisely what I needed~~